Providing data of a memory system based on an adjustable error rate

ABSTRACT

A first data stored at a first portion of a memory cell and a second data stored at a second portion of the memory cell are identified. A first error rate associated with first data stored at the first portion of the memory cell is determined. The first error rate is adjusted to exceed a second error rate associated with the second data stored at the second portion of the memory cell. A determination is made as to whether the first error rate exceeds a threshold. The second data stored at the second portion of the memory cell is provided for use in an error correction operation by a controller associated with the memory cell in response to determining that the first error rate exceeds the threshold.

RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 15/914,402, filed Mar. 7, 2018, which is hereinincorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to a memory system, and morespecifically, relates to providing data of a memory system based on anadjustable error rate.

BACKGROUND

A memory system can be a storage system, such as a solid-state drive(SSD), and can include one or more memory components that store data.For example, a memory system can include memory devices such asnon-volatile memory devices and volatile memory devices. In general, ahost system can utilize a memory system to store data at the memorydevices of the memory system and to retrieve data stored at the memorysystem.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousimplementations of the disclosure.

FIG. 1 illustrates an example computing environment that includes amemory system in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a flow diagram of an example method to provide additional dataof a memory system based on an adjustable error rate exceeding athreshold in accordance with some embodiments of the present disclosure.

FIG. 3 is a flow diagram of an example method to perform an errorcorrection operation on data based on a read operation performed onanother data in accordance with some embodiments of the presentdisclosure.

FIG. 4A illustrates an example of initial program verify voltages forlevels of a memory cell in accordance with one embodiment of the presentdisclosure.

FIG. 4B illustrates an example of adjusting program verify voltages toincrease or decrease the error rates of data stored at portions of thememory cell in accordance with some embodiments of the presentdisclosure.

FIG. 5A illustrates an example of providing data from a memory cell of amemory system based on an adjustable error rate in accordance with someembodiments of the present disclosure.

FIG. 5B illustrates an example of providing additional data of thememory system based on an adjustable error rate in accordance with someembodiments of the present disclosure.

FIG. 6 is a block diagram of an example computer system in whichimplementations of the present disclosure may operate.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed to providing data of amemory system based on an adjustable error rate. An example of a memorysystem is a storage system, such as a solid-state drive (SSD). In someembodiments, the memory system is a hybrid memory/storage system. Ingeneral, a host system can utilize a memory system that includes one ormore memory devices. The memory devices can include non-volatile memorydevices, such as, for example, negative-and (NAND). The host system canprovide data to be stored at the memory system and can request data tobe retrieved from the memory system.

The memory system can store the data at memory cells of a memory deviceincluded in the memory system. Each of the memory cells can store one ormore bits of binary data corresponding to the data received from thehost system. The memory device can include a quad-level cell (QLC)memory. In QLC memory, each memory cell can store four bits of data. Forexample, in a QLC memory, a memory cell can store four bits of data(e.g., 1111, 0000, 1101, etc.) corresponding to data received from thehost system. Each bit of the memory cell is stored at a differentportion (also referred to as “page” hereafter) of the memory cell. Amemory cell of the QLC memory can have a total of four pages. Forexample, the memory cell can include a lower page (LP), an upper page(UP), an extra page (XP) and a top page (TP), where each page stores abit of data. For example, a bit can be represented by each of the fourpages of the memory cell. In a memory cell for a QLC memory, eachcombination of four bits can correspond to a different voltage level(also referred to as “level” hereafter). For example, a first level ofthe memory cell can correspond to 1111, a second level can correspond to0111, and so on. Because a memory cell for a QLC memory includes 4 bitsof data, there are a total of 16 possible combinations of the four bitsof data. Accordingly, a memory cell for a QLC memory can be programmedto one of 16 different levels.

Generally, the memory system receives a request from a host system toperform a programming operation to store data at the QLC memory. Acontroller of the memory system can store the data by performing atwo-pass programming operation on the memory cells of the memory system.During a first programming pass of the two-pass programming operation,the controller programs a number of pages to a memory cell. For example,the controller can apply a voltage level to the memory cell to programthree pages of data from the host system to the memory cell. The secondprogramming pass can then be performed on the memory cell.

The second programming pass programs the last page of the memory cell.The level that the memory cell is programmed to in the secondprogramming pass can be based on the last page of the memory cell aswell as the prior pages that were programmed at the memory cell in thefirst programming pass. Therefore, if data stored at any of the pages ofthe memory cell during the first programming pass includes an error andthe error is not corrected before the second programming pass isperformed on the memory cell, then the memory cell will be programmed tothe wrong level (also referred to as “level misplacement” hereafter),resulting in an increased error rate for the data stored at the memorycell. These types of errors can be considered as write-in errors, wherethe wrong data is written to the memory cell. Level misplacements canresult in high reliability errors of the data stored at the memory cell,which can deteriorate the performance of the memory system if a largenumber of error correction operations are to be performed. Accordingly,after programming the first three of the four portions of a memory cellof a QLC memory during the first programming pass, in the secondprogramming pass the memory system can determine whether data stored atthe first three portions includes an error by providing the data to thecontroller. In one example of a conventional memory system, a readoperation is performed on the three portions of the memory cell duringthe second programming pass. For example, the controller performs theread operation on data at the three pages of the memory cell that wasprogrammed during the first programming pass. The read operation is usedto correct the bit errors at any of the pages and determine thecorresponding error rate associated with the data stored at the memorycell. Thus, when a conventional memory system provides the three pagesassociated with the first pass to the controller, then second passprograming of the conventional memory system can be performed using thelast page provided by the host system and the three corrected pages atthe controller. This can result in no level misplacement or a reducedlevel misplacement. The corrected data can be programmed to the memorycell along with data to be programmed to the remaining page of thememory cell that is received from the host system during the secondprogramming pass. However, an interface used by the controller of thememory system can be shared between multiple memory devices that includememory cells. The interface can have a limited bandwidth that isavailable for input/output (TO) operations performed by the controlleron the memory devices. Accordingly, performing IO operations thatutilize a large amount of the bandwidth, such as the read operations onthe three pages of multiple memory cells associated with the firstprogramming pass, can result in a saturation of the interface (e.g., thebandwidth of IO operations exceeds the available bandwidth of theinterface). In one example of a conventional memory system, the datastored at all three pages of the memory cell are read internally andstored locally at a buffer of the memory device without providing thedata to the controller via the interface. In such an example, the firstprogramming pass includes three IO operations (one IO operation perpage) and the second programming pass includes one IO operation toprogram the remaining page for a total of four IO operations beingperformed via the interface. While such an example can reduce the numberof IO operations being performed via the interface, the probability oflevel misplacement increases by not providing any of the data of thefirst programming pass to the controller for error correction.

In another example of a conventional memory system, the data stored atall three pages of the first programming pass is sent to the controllervia the interface. In such an example, the first programming passincludes three IO operations to program the first three pages andproviding the data stored at all three pages to the controller utilizesanother three IO operations. The second programming pass includes fourIO operations (e.g., 3 IO operations for the three pages provided to thecontroller and 1 IO operation to program data received from the hostsystem to the remaining page), resulting in a total of 10 IO operationsbeing performed via the interface. This increased number of IOoperations performed via the interface can cause a bottleneck of IOoperations at the interface that can be performed at the rate ofavailable bandwidth of the interface, resulting in an increase inlatency and a decrease in performance of the memory system.

Alternatively, in another example of a conventional memory system,rather than the memory system performing a read operation on the datastored at the three portions of the memory cell, the data stored at thethree portions can additionally be stored locally on a buffer memory ofa controller of the memory system during the first programming pass toreduce the number of IO operations being performed via the interface. Insuch an example, the first programming pass includes three IO operationsto program the first three pages and the second programming passincludes four IO operations (e.g., 3 IO operations for the three pagesstored locally on the buffer of the controller and 1 IO operation toprogram data received from the host system to the remaining page),resulting in a total of 7 IO operations being performed via theinterface. However, storing the data locally on the controller canresult in additional components being added to the controller, such as abuffer memory to store the data provided to the memory cell. This canresult in an increase in the cost and complexity of the memory system.

Aspects of the present disclosure address the above and otherdeficiencies by providing data to a controller based on an error rate.The first data stored at the first portion of the memory cell isprovided to a controller of the memory system. The controller firstcorrects any errors at the first data and determines an error rateassociated with the first data. The first data may be data from aparticular page of a group of pages that was programmed during a firstprogramming pass The controller determines whether the error rateassociated with the first data exceeds a threshold. In one embodiment,the error rate associated with the first page can be used as a proxy forother data from the other two pages that was programmed during the firstprogramming pass. This use of the error rate of the first page as aproxy for the other data from the other pages programmed during thefirst programming pass can be utilized in the second programming pass.For example, the three pages programmed during the first programmingpass can have similar error and disturb mechanisms. Therefore, anelevated error rate for the first page can also indicate an elevatederror rate for the data at the other two pages programmed in the firstprogramming pass. Because the first data stored at the first portion ofthe memory cell (e.g., the first page) is programmed during the firstprogramming pass with the second data at the second portion (e.g., thesecond page), the error rate of the first data can be used to determinewhether the second data likely includes an error. For example, if theerror rate exceeds the threshold, indicating a relatively high errorrate associated with the first data, then the second data stored at thememory cell can also have a relatively high error rate. Accordingly, ifthe memory system determines that the error rate exceeds the threshold,then the second data stored at the second portion of the memory cell isprovided to the controller of the memory system for error correction.Such a process can ensure that first and second pages will not includelevel misplacement when the second programming pass is performed.

Thus, providing data to a controller based on determined error rates canresult in improved system performance of the memory system by providingsecond data from a second portion of the memory cell to a controllerwhen an error rate of first data at a first portion of memory cellexceeds a threshold. Accordingly, the number of TO operations beingperformed via the interface of the memory system can be reduced byproviding the second data via the interface when the error rate exceedsa threshold and the occurrence of bottlenecks at the interface caused bythe TO operations can be reduced or eliminated. Furthermore, additionalcomponents, such as a buffer memory for the storage of data (e.g., firstdata and second data), are not added to the controller. Additionally,the number of level misplacements is reduced because data stored atpages having a high error rate are provided to the controller for errorcorrection. As a result, the performance of the storage device can beimproved by decreasing the latency of the storage device without theaddition of hardware components to the memory controller. Although thepresent examples describe providing data to a controller based ondetermined error rates during a second programming pass of a memory cellof a QLC memory, aspects of the present disclosure can be applied to anyprogramming operation of a memory cell of a memory system that includesmultiple (e.g., two or more) bits of data. Furthermore, although thepresent examples describe providing data to a controller based ondetermined error rates during the second programming pass of a memorycell of QLC memory, aspects of the present disclosure can be applied toany number (e.g., one or more) programming operations for any type ofmemory.

FIG. 1 illustrates an example computing environment 100 that includes amemory system 110 in accordance with some implementations of the presentdisclosure. The memory system 110 can include media, such as memorydevices 112A to 112N. The memory devices 112A to 112N can be volatilememory devices, non-volatile memory devices, or a combination of such.In some embodiments, the memory system is a storage system. An exampleof a storage system is a SSD. In general, the computing environment 100can include a host system 120 that uses the memory system 110. In someimplementations, the host system 120 can write data to the memory system110 and read data from the memory system 110. In some embodiments, thememory system 110 is a hybrid memory/storage system.

The host system 120 can be a computing device such as a desktopcomputer, laptop computer, network server, mobile device, or suchcomputing device that includes a memory and a processing device. Thehost system 120 can include or be coupled to the memory system 110 sothat the host system 120 can read data from or write data to the memorysystem 110. The host system 120 can be coupled to the memory system 110via a physical host interface. As used herein, “coupled to” generallyrefers to a connection between components, which can be an indirectcommunicative connection or direct communicative connection (e.g.,without intervening components), whether wired or wireless, includingconnections such as, electrical, optical, magnetic, etc. Examples of aphysical host interface include, but are not limited to, a serialadvanced technology attachment (SATA) interface, a peripheral componentinterconnect express (PCIe) interface, universal serial bus (USB)interface, Fibre Channel, Serial Attached SCSI (SAS), etc. The physicalhost interface can be used to transmit data between the host system 120and the memory system 110. The host system 120 can further utilize anNVM Express (NVMe) interface to access the memory devices 112A to 112Nwhen the memory system 110 is coupled with the host system 120 by thePCIe interface. The physical host interface can provide an interface forpassing control, address, data, and other signals between the memorysystem 110 and the host system 120.

The memory devices 112A to 112N can include any combination of thedifferent types of non-volatile memory devices and/or volatile memorydevices. An example of non-volatile memory devices includes anegative-and (NAND) type flash memory. Each of the memory devices 112Ato 112N can include one or more arrays of memory cells such as singlelevel cells (SLCs) or multi-level cells (MLCs) (e.g., triple level cells(TLCs) or quad-level cells (QLCs)). In some implementations, aparticular memory device can include both an SLC portion and a MLCportion of memory cells. Each of the memory cells can store bits of data(e.g., data blocks) used by the host system 120. Although non-volatilememory devices such as NAND type flash memory are described, the memorydevices 112A to 112N can be based on any other type of memory such as avolatile memory. In some implementations, the memory devices 112A to112N can be, but are not limited to, random access memory (RAM),read-only memory (ROM), dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), phase change memory (PCM), magnetorandom access memory (MRAM), negative-or (NOR) flash memory,electrically erasable programmable read-only memory (EEPROM), and across-point array of non-volatile memory cells. A cross-point array ofnon-volatile memory can perform bit storage based on a change of bulkresistance, in conjunction with a stackable cross-gridded data accessarray. Additionally, in contrast to many Flash-based memory, cross pointnon-volatile memory can perform a write in-place operation, where anon-volatile memory cell can be programmed without the non-volatilememory cell being previously erased. Furthermore, the memory cells ofthe memory devices 112A to 112N can be grouped as memory pages or datablocks that can refer to a unit of the memory device used to store data.

The controller 115 can communicate with the memory devices 112A to 112Nto perform operations such as reading data, writing data, or erasingdata at the memory devices 112A to 112N and other such operations. Thecontroller 115 can include hardware such as one or more integratedcircuits and/or discrete components, a buffer memory, or a combinationthereof. The controller 115 can be a microcontroller, special purposelogic circuitry (e.g., a field programmable gate array (FPGA), anapplication specific integrated circuit (ASIC), etc.), or other suitableprocessor. The controller 115 can include a processor (processingdevice) 117 configured to execute instructions stored in local memory119. In the illustrated example, the local memory 119 of the controller115 includes an embedded memory configured to store instructions forperforming various processes, operations, logic flows, and routines thatcontrol operation of the memory system 110, including handlingcommunications between the memory system 110 and the host system 120. Insome embodiments, the local memory 119 can include memory registersstoring, e.g., memory pointers, fetched data, etc. The local memory 119can also include read-only memory (ROM) for storing micro-code. Whilethe example memory system 110 in FIG. 1 has been illustrated asincluding the controller 115, in another embodiment of the presentdisclosure, a memory system 110 may not include a controller 115, andmay instead rely upon external control (e.g., provided by an externalhost, or by a processor or controller separate from the memory system).

In general, the controller 115 can receive commands or operations fromthe host system 120 and can convert the commands or operations intoinstructions or appropriate commands to achieve the desired access tothe memory devices 112A to 112N. The controller 115 can be responsiblefor other operations such as wear leveling operations, garbagecollection operations, error detection and error-correcting code (ECC)operations, encryption operations, caching operations, and addresstranslations between a logical block address and a physical blockaddress that are associated with the memory devices 112A to 112N. Thecontroller 115 can further include host interface circuitry tocommunicate with the host system 120 via the physical host interface.The host interface circuitry can convert the commands received from thehost system into command instructions to access the memory devices 112Ato 112N as well as convert responses associated with the memory devices112A to 112N into information for the host system 120.

The memory system 110 can include an error determining component 113that can be used to determine error rates for data stored at memorycells of the memory system. The error rate can be determined bycomparing the data read from the memory cell and comparing it withoutput data associated with an error correction operation performed onthe data. In some embodiments, the controller 111 includes at least aportion of the error determining component 113. The error determiningcomponent 113 can determine error rates associated with the data readfrom the memory. The error rates for the data can correspond to aprobability that the data stored at a memory cell includes an error. Theerror determining component 113 can determine an error rate that isassociated with first data stored at a first portion of a memory cell ofone of the memory devices 112A-N of the memory system 110. For example,the error determining component 113 can determine the error rate forfirst data stored at the first page of a memory cell that is provided tothe controller. Further details with regards to the operations of theerror determining component 113 are described below.

In some implementation, the data structure can be a table or other typesof data structures to store the write attributes for memory pages in thefirst region. In some implementations, the table can include acorresponding entry for each memory page associated with data written tothe first region. As data from the host system 120 is received to bestored at the memory devices 112A to 112N, the write attribute handler113 can receive and store an indication of a temperature measurementtaken at the time the data is programmed to the memory devices 112A to112N. After the pages are programed, the measured temperature is storedon a page in a SLC page in the memory. By storing the write attributesin the SLC page, the controller 115 can determine, for example, whetherthere is an extreme shift in temperature from when the data wasprogrammed at a memory cell to when it was subsequently read from thatmemory cell.

The memory system 110 can also include additional circuitry orcomponents that are not illustrated. In some implementations, the memorysystem 110 can include a cache or buffer (e.g., DRAM) and addresscircuitry (e.g., a row decoder and a column decoder) that can receive anaddress from the controller 115 and decode the address to access thememory devices 112A to 112N.

FIG. 2 is a flow diagram of an example method 200 to provide second datato a controller based on an adjusted error rate exceeding a threshold,in accordance with some embodiments of the present disclosure. Themethod 200 can be performed by processing logic that can includehardware (e.g., processing device, circuitry, dedicated logic,programmable logic, microcode, hardware of a device, integrated circuit,etc.), software (e.g., instructions run or executed on a processingdevice), or a combination thereof. In some implementations, the method200 is performed by the error determining component 113 of FIG. 1. Inanother implementation, the method 200 can be performed by a host system(e.g., host system 120 of FIG. 1) having access to modify parameters ofthe memory device.

At block 210, a processing device identifies a first data stored at afirst portion of a memory cell and a second data stored at a secondportion of the memory cell. For example, the processing deviceidentifies first data stored at the first page of a memory cell andsecond data stored at the second page of the memory cell. At block 220,an error rate associated with the first data is determined. In oneembodiment, the error rate can be determined by comparing the first datathat is provided to the controller with output data of an errorcorrection operation associated with the first data. In embodiments, theerror rate can be greater than an expected error rate of the seconddata. As previously discussed, by having the error rate of the firstdata be greater than an error rate associated with a second or otherdata stored at the memory cell, the first data can act as a proxy forthe second data. For example, if the first data has a high error rate,then the second data can also be assumed to have a high error rate.Thus, if data at three portions (e.g., pages) of a memory cell areprogrammed, the error rate of the data at a particular portion of thethree portions can be higher than the error rate at the other data atthe remaining portions of the three portions of the memory cell.

Accordingly, in some embodiments, the error rate associated with thefirst data stored at the first portion of the memory cell can beadjusted so that it is greater than the error rate associated with thesecond data (or any other data programmed during the first programmingpass). The adjustment of the error rate can be based on the adjusting ofprogram verify (PV) voltages for corresponding levels of the memorycell. The PV voltage for a particular level corresponds to a targetvoltage threshold, such each memory cell at the particular level has avoltage threshold that exceeds the PV voltage. For example, if aparticular level has a PV voltage of PV1, then the memory cellsprogrammed to the particular level can have a voltage threshold that isgreater than PV1. The PV voltages can be adjusted such that a desirableordering between page error rates can be achieved. The operation toadjust the PV voltages (also referred to as a dynamic programming target(DPT) operation hereafter) can be performed over time. The input of theDPT operation uses page error rates and iteratively adjusts PV voltagesassociated with particular pages of a memory cell in an iterativeprocess to achieve a desired error rate between different pages of thememory cell. A DPT operation can adjust the PV voltages associated withthe memory cell so that a subsequent error rate associated with thefirst data stored at the memory cell can be expected to be greater thana subsequent error rate associated with the other data stored at thememory cell. For example, the DPT operation can decrease the range ofthe PV voltage associated with the data stored at the memory cell and/orincrease the range of the PV voltage associated with the other datastored at the memory cell to ensure that the subsequent error rateassociated with the data is greater than the subsequent error rateassociated with the other data. Further detail regarding the adjustmentof PV voltages are described below in conjunction with FIGS. 4A and 4B

At block 230, the processing device determines whether the error rateexceeds a threshold. The first error rate may be expected to be largerthan other error rates for other data stored at the memory cell. In oneimplementation, a read operation can be performed on the first datastored at the first portion of the memory cell. The first data from theread operation can be provided to a controller of the memory system andthe controller can determine whether the error rate for the first dataexceeds the threshold. At block 240, in response to determining that theerror rate exceeds the threshold, the second data stored at the secondportion of the memory cell is provided for use in an error correctionoperation. For example, the second data stored at the second page of thememory cell that was programmed during the first programming pass isprovided to the controller (e.g., controller 111 of FIG. 1) for errorcorrection. In one implementation, the second data stored at the secondpage of the memory cell can be provided to the controller during asecond programming pass of a two-pass programming operation. In someimplementations, an error correction operation is performed on thesecond data, as will be discussed in more detail below. Inimplementations, third data stored at a third portion of the memory cellcan be provided for use in an error correction operation in response tothe error rate exceeding a threshold. For example, third data stored ata third page of the memory cell can be provided to the controller. Thecontroller can determine whether the third data includes an error. Ifthe controller determines the third data includes an error, thecontroller can perform an error correction data on the third data tocorrect the error.

As such, when an error rate for a particular data stored at a memorycell during a first programming pass exceeds a threshold rate, otherdata stored at the memory cell during the first programming pass can beretrieved and provided for use in an error correction operation. Theerror correction operation can be performed on the data stored at thememory cell as part of the second programming pass.

FIG. 3 is a flow diagram of an example method 300 to perform an errorcorrection operation on data based on a read operation performed onanother data, in accordance with some embodiments of the presentdisclosure. The method 300 can be performed by processing logic that caninclude hardware (e.g., processing device, circuitry, dedicated logic,programmable logic, microcode, hardware of a device, integrated circuit,etc.), software (e.g., instructions run or executed on a processingdevice), or a combination thereof. In some implementations, the method300 can be performed by the error determining component 113 of FIG. 1.In another implementation, the method 200 can be performed by a hostsystem (e.g., host system 120 of FIG. 1) having access to modifyparameters of the memory device.

At block 310, a processing device performs a read operation on firstdata stored at a first portion of a memory cell. For example, a readoperation is performed on first data stored at the first page of amemory cell. At block 320, an error rate associated with the first datastored at a first portion of the memory cell is adjusted to that theerror rate associated with the first data is greater than an error rateassociated with second data that is stored at a second portion of thememory cell. The error rates can be adjusted by modifying associated PVvoltage values, as will be described below. At block 330, an error rateassociated with the first data is determined to exceed a threshold. Atblock 340, in response to determining that the error rate exceeds thethreshold, second data stored at a second portion of the memory cell isprovided for use in an error correction operation. For example, seconddata stored at the second page of the memory cell can be provided to thecontroller for error correction.

At block 350, the error correction operation is performed on the seconddata. In some implementations, an error-correcting code (ECC) operationor another type of error detection and correction operation can be usedto detect and correct the error. For example, if the data read at thefirst page of the memory cell corresponds to a value of 1, the error canbe corrected by changing the value from a 1 to a 0. In implementations,the first data can be determined to include an error. If the first datais determined to include an error, then an error correction operationcan be performed on the first data. At block 360, the corrected seconddata is provided to the second portion of the memory cell. For example,the corrected second data is provided to the second page of the memorycell for storage. In some implementations, the first data or correctedfirst data is provided to the first page of the memory cell. Inimplementations, the remaining page of the memory cell programmed duringthe second programming pass can be programmed based on the correcteddata that is provided to the first page and/or second page of the memorycell.

FIG. 4A illustrates an example of initial program verify voltages 400for levels of a memory cell, in accordance with one embodiment of thepresent disclosure. As shown, a memory cell that stores two bits of dataincludes four levels L0, L1, L2, and L3 that can be programmed withthree PV voltages (e.g., PV1 for L1, PV2 for L2 and PV3 for L3). In thisexample, the valley margin between L1 and L2 (D2) determines an expectederror rate for data stored at a portion of the memory cell and thevalley margin between L0 and L1 (D1) and L2 and L3 (D3) determine theerror rate for data stored at another portion of the memory cell.

FIG. 4B illustrates an example of adjusting program verify voltages 450to increase or decrease the error rates of data stored at portions thememory cell, in accordance with some embodiments of the presentdisclosure. As shown, the error rate for the data stored at the portionof the memory cell is to be decreased so that the error rate for thedata stored at the portion of the memory cell is less than the errorrate for the data stored at the other portion of the memory cell. Forexample, PV2 can be shifted to the right (e.g., PV2A), which decreasesthe valley margin D3 between shifted L2 and L3 while also increasing thevalley margin D2 between L1 and L2. The result is a decrease in theerror rate associated with the data stored at the portion of the memorycell by increasing the distance D2 associated with data stored at thefirst portion of the memory cell. Furthermore, the expected error rateassociated with the data stored at the other portion of the memory cellis increased by decreasing the distance D3 associated with the errorrate for data stored at the second portion of the memory cell.

In another example, PV1 can be shifted to the left (e.g., PV1A), whichdecreases valley margin D1 between shifted L1 and L0 and increasesdistance D2 valley margin shifted L1 and L2. This results in a decreasein the error rate associated with the data stored at the portion of thememory cell by increasing the distance D2 associated with data stored atthe portion of the memory cell. Furthermore, the error rate associatedwith the data stored at the other portion of the memory cell isincreased by decreasing the distance D1 associated with the error ratefor data stored at the other portion of the memory cell.

FIG. 5A illustrates an example of providing data from a memory cell of amemory system 500 based on an adjustable error rate, in accordance withsome embodiments of the present disclosure. The memory system 500includes a memory cell 530 and a controller 510 that corresponds tocontroller 111 of FIG. 1. Although the present illustration discussesproviding data to a controller of the memory system based on anadjustable error rate, in other embodiments the data can be provided toother components of the computing environment 100 of FIG. 1. Forexample, the data can be provided to host system 120 of FIG. 1 so thatthe host system can provide the error correction for the data. Thememory cell 530 can include first data 540 a stored at a first portion(e.g., the first page) of the memory cell 530 and second data 545 astored at a second portion (e.g., the second page) of the memory cell530. As previously discussed, a read operation can be performed onmemory cell 530 as part of a first programming pass of a two-passprogramming process. During the read operation, first data 540 b can beprovided to controller 510. First data 540 b can be a copy of first data540 a read from memory cell 530. Upon receiving the first data 540 b,the memory system can determine whether a first error rate associatedwith the first data 540 b exceeds a threshold when a controller 510performs an error correction operation on first data 540 b.

FIG. 5B illustrates an example of providing additional data of thememory cell of the memory system, in accordance with some embodiments ofthe present disclosure. If the first error rate associated with firstdata 540 b exceeds a threshold, then second data 545 b is read from amemory device 520 associated with memory cell 530 to controller 510.Upon receipt of second data 545 b, the controller 510 determines whethersecond data 545 b includes any errors. If controller 510 determines thatsecond data 545 b includes errors, then controller 510 can perform anerror correction operation on second data 545 b. The controller providescorrected first data and/or second data to memory cell 530. For example,the corrected first data can be provided to the first page of the memorycell and/or the corrected second data can be provided to the second pageof the memory cell. In some implementations, controller 510 candetermine that first data 540 b and/or second data 545 b do not includeany errors. Accordingly, the controller 510 can provide first data 540 band/or second data 545 b to memory cell 530 to refresh the portions ofthe data stored at memory cell 530.

FIG. 6 illustrates an example machine of a computer system 600 withinwhich a set of instructions, for causing the machine to perform any oneor more of the methodologies discussed herein, may be executed. Forexample, the computer system 600 may correspond to a host system (e.g.,the host system 120 of FIG. 1) that includes or utilizes a memory system(e.g., the memory system 110 of FIG. 1) or may be used to perform theoperations of a controller (e.g., to execute an operating system toperform operations corresponding to the error determining component 113of FIG. 1). In alternative implementations, the machine may be connected(e.g., networked) to other machines in a LAN, an intranet, an extranet,and/or the Internet. The machine may operate in the capacity of a serveror a client machine in client-server network environment, as a peermachine in a peer-to-peer (or distributed) network environment, or as aserver or a client machine in a cloud computing infrastructure orenvironment.

The machine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, a switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated, the term “machine” shall also betaken to include any collection of machines that individually or jointlyexecute a set (or multiple sets) of instructions to perform any one ormore of the methodologies discussed herein.

The example computer system 600 includes a processing device 602, a mainmemory 604 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM(RDRAM), etc.), a static memory 606 (e.g., flash memory, static randomaccess memory (SRAM), etc.), and a data storage system 618, whichcommunicate with each other via a bus 630.

Processing device 602 represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device may be a complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice 602 may also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. The processing device 602 is configuredto execute instructions 626 for performing the operations and stepsdiscussed herein. The computer system 600 may further include a networkinterface device 608 to communicate over the network 620.

The data storage system 618 may include a machine-readable storagemedium 624 (also known as a computer-readable medium) on which is storedone or more sets of instructions or software 626 embodying any one ormore of the methodologies or functions described herein. Theinstructions 626 may also reside, completely or at least partially,within the main memory 604 and/or within the processing device 602during execution thereof by the computer system 600, the main memory 604and the processing device 602 also constituting machine-readable storagemedia. The machine-readable storage medium 624, data storage system 618,and/or main memory 604 may correspond to the memory system 110 of FIG.1.

In one implementation, the instructions 626 include instructions toimplement functionality corresponding to an error determining component(e.g., error determining component 113 of FIG. 1). While themachine-readable storage medium 624 is shown in an exampleimplementation to be a single medium, the term “machine-readable storagemedium” should be taken to include a single medium or multiple mediathat store the one or more sets of instructions. The term“machine-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine and that cause the machine to perform any oneor more of the methodologies of the present disclosure. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, optical media, and magneticmedia.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure may refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for theintended purposes, or it may include a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages may be used to implement the teachings of thedisclosure as described herein.

The present disclosure may be provided as a computer program product, orsoftware, that may include a machine-readable medium having storedthereon instructions, which may be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). Forexample, a machine-readable (e.g., computer-readable) medium includes amachine (e.g., a computer) readable storage medium such as a read onlymemory (“ROM”), random access memory (“RAM”), magnetic disk storagemedia, optical storage media, flash memory devices, etc.

In the foregoing specification, implementations of the disclosure havebeen described with reference to specific example implementationsthereof. It will be evident that various modifications may be madethereto without departing from the broader spirit and scope ofimplementations of the disclosure as set forth in the following claims.The specification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

What is claimed is:
 1. A system comprising: a memory device; and aprocessing device, operatively coupled with the memory device, to:identify a first data stored at a first portion of a memory cell and asecond data stored at a second portion of the memory cell; determine afirst error rate associated with the first data stored at the firstportion of the memory cell, the first error rate being adjusted toexceed a second error rate associated with the second data stored at thesecond portion of the memory cell; determine whether the first errorrate exceeds a threshold; and in response to determining that the firsterror rate exceeds the threshold, provide the second data stored at thesecond portion of the memory cell for use in an error correctionoperation by a controller associated with the memory cell.
 2. The systemof claim 1, wherein the processing device is further to: perform theerror correction operation on the second data stored at the secondportion of the memory cell; and provide the corrected second data to thesecond portion of the memory cell.
 3. The system of claim 2, wherein thecorrected second data is provided to the second portion of the memorycell during a second programming operation performed on the memory cell.4. The system of claim 1, wherein the first error rate associated withthe first data stored at the first portion of the memory cell is basedon a first programming operation performed on the memory cell.
 5. Thesystem of claim 1, wherein the processing device is further to: performa read operation on the first data stored at the first portion of thememory cell; and provide the first data stored at the first portion ofthe memory cell to the controller associated with the memory cell,wherein determining whether the first error rate exceeds the thresholdis based on providing the first data stored at the first portion of thememory cell to the controller associated with the memory cell.
 6. Thesystem of claim 1, wherein to determine the first error rate associatedwith the first data stored at the first portion of the memory cell, theprocessing device is further to: adjust the first error rate associatedwith the first data stored at the first portion of the memory cell bymodifying one or more program voltages associated with the first datastored at the first portion of the memory cell.
 7. The system of claim6, wherein to adjust the first error rate associated with the first datastored at the first portion of the memory cell, the processing device isfurther to modify the one or more program voltages to increase asubsequent first error rate, and wherein the modifying the one or moreprogram voltages to increase the subsequent first error rate correspondsto a decrease in a subsequent second error rate associated with thesecond data stored at the second portion of the memory cell.
 8. A methodcomprising: identifying a first data stored at a first portion of amemory cell and a second data stored at a second portion of the memorycell; determining a first error rate associated with the first datastored at the first portion of the memory cell, the first error ratebeing adjusted to exceed a second error rate associated with the seconddata stored at the second portion of the memory cell; determiningwhether the first error rate exceeds a threshold; and in response todetermining that the first error rate exceeds the threshold, providing,by a processing device, the second data stored at the second portion ofthe memory cell for use in an error correction operation by a controllerassociated with the memory cell.
 9. The method of claim 8, furthercomprising: performing the error correction operation on the second datastored at the second portion of the memory cell; and providing thecorrected second data to the second portion of the memory cell.
 10. Themethod of claim 9, wherein the corrected second data is provided to thesecond portion of the memory cell during a second programming operationperformed on the memory cell.
 11. The method of claim 8, wherein thefirst error rate associated with the first data stored at the firstportion of the memory cell is based on a first programming operationperformed on the memory cell.
 12. The method of claim 8, furthercomprising: performing a read operation on the first data stored at thefirst portion of the memory cell; and providing the first data stored atthe first portion of the memory cell to the controller associated withthe memory cell, wherein determining whether the first error rateexceeds the threshold is based on providing the first data stored at thefirst portion of the memory cell to the controller associated with thememory cell.
 13. The method of claim 8, wherein determining the firsterror rate associated with the first data stored at the first portion ofthe memory cell further comprises: adjusting the first error rateassociated with the first data stored at the first portion of the memorycell by modifying one or more program voltages associated with the firstdata stored at the first portion of the memory cell.
 14. The method ofclaim 13, wherein adjusting the first error rate associated with thefirst data stored at the first portion of the memory cell furthercomprises modifying the one or more program voltages to increase asubsequent first error rate, and wherein the modifying the one or moreprogram voltages to increase the subsequent first error rate correspondsto a decrease in a subsequent second error rate associated with thesecond data stored at the second portion of the memory cell.
 15. Anon-transitory computer-readable storage medium comprising instructionsthat, when executed by a processing device, cause the processing deviceto: identify a first data stored at a first portion of a memory cell anda second data stored at a second portion of the memory cell; determine afirst error rate associated with the first data stored at the firstportion of the memory cell, the first error rate being adjusted toexceed a second error rate associated with the second data stored at thesecond portion of the memory cell; determine whether the first errorrate exceeds a threshold; and in response to determining that the firsterror rate exceeds the threshold, provide the second data stored at thesecond portion of the memory cell for use in an error correctionoperation by a controller associated with the memory cell.
 16. Thenon-transitory computer-readable storage medium of claim 15, wherein theprocessing device is further to: perform the error correction operationon the second data stored at the second portion of the memory cell; andprovide the corrected second data to the second portion of the memorycell.
 17. The non-transitory computer-readable storage medium of claim16, wherein the corrected second data is provided to the second portionof the memory cell during a second programming operation performed onthe memory cell.
 18. The non-transitory computer-readable storage mediumof claim 15, wherein the first error rate associated with the first datastored at the first portion of the memory cell is based on a firstprogramming operation performed on the memory cell.
 19. Thenon-transitory computer-readable storage medium of claim 15, wherein todetermine the first error rate associated with the first data stored atthe first portion of the memory cell, the processing device is furtherto: adjust the first error rate associated with the first data stored atthe first portion of the memory cell by modifying one or more programvoltages associated with the first data stored at the first portion ofthe memory cell.
 20. The non-transitory computer-readable storage mediumof claim 19, wherein to adjust the first error rate associated with thefirst data stored at the first portion of the memory cell, theprocessing device is further to modify the one or more program voltagesto increase a subsequent first error rate, and wherein the modifying theone or more program voltages to increase the subsequent first error ratecorresponds to a decrease in a subsequent second error rate associatedwith the second data stored at the second portion of the memory cell.21. The non-transitory computer-readable storage medium of claim 15,wherein the processing device is further to: in response to determiningthat the first error rate exceeds the threshold, provide third datastored at a third portion of the memory cell to the controllerassociated with the memory cell.